xii MECHANICS OF RESPIRATION 427 



about J smaller than in adults. In expiration a weak and c^uiet 

 murmur is heard. 



In auscultating along the larger respiratory passages (larynx, 

 trachea, great bronchi), both in inspiration and in expiration a 

 harsh murmur is heard, sharp and clear, resembling the guttural 

 German cli, which is known as the bronchial murmur. This is 

 perceptible not merely in the neck, along the larynx and trachea, 

 but also in the thorax between the two shoulder-blades at the 

 le.vel of the fourth dorsal vertebra, the point at which the bronchi 

 bifurcate. It is a little more accentuated on the right side, 

 because the right bronchus is of greater calibre and is stronger as 

 a rule in expiration than in inspiration. In the other parts of the 

 thorax the bronchial murmur is imperceptible, being covered by 

 the vesicular murmur. But it is heard distinctly in certain parts 

 of the pulmonary area, when the alveoli are atelectatic or 

 infiltrated. In pneumonia, accordingly, the area of lung that 

 has become impervious to air, or hepatised, (-an be determined 



FIG. li0. Respiratory oscillations of intruthoracic pressure (T) ami intra-abdominal pressure (A 

 in anaesthetised cloy;. (Luciaiii.) 



from the extent of the region in which the bronchial murmur 

 is abnormally audible. 



X. As above stated it is not only the lungs, but also the heart 

 and blood-vessels that feel the effects of the changes in pressure 

 determined by respiratory rhythm. 



To obtain an exact knowledge of these effects it is necessary 

 first to study the oscillations of intrathoracic and intra-abdominal 

 pressure in the two periods of the respiratory cycle or revolution. 

 This is most simply effected by the method of the oesophageal or 

 rectal sound, in conjunction with Marey's recording tambour 

 (Luciani, 1878 ; Rosenthal, 1880). 



The tracings of Fig. 190, which we obtained by this method 

 from an anaesthetised dog, are highly instructive, since they show 

 that the respiratory oscillations of pressure within the thorax and 

 abdomen are not coincident but interfering. While intrathoracic 

 pressure falls during inspiration and rises in expiration, i intra- 

 abdominal pressure rises in the first period of inspiration and 

 falls in the second, and falls in the first period of expiration and 



